1. Technical Field
The embodiments herein generally relate to a multi-chip antenna diversity architecture, and more particularly to, a multi-chip antenna diversity and picture-in-picture architecture.
2. Description of the Related Art
Antenna diversity is a wireless diversity scheme that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight (LOS) between a transmitter and a receiver. Instead the signal is reflected along multiple paths before finally being received. Each of these bounces can introduce phase shifts, time delays, attenuations, and even distortions that can destructively interfere with one another at the aperture of the receiving antenna. Antenna diversity is especially effective at mitigating multipath situations.
Mobile television receivers can be integrated into a variety of devices ranging from low cost low performance products to the high cost high performance products. It is possible to design a single chip to address both ends of the market by creating a multi-chip diversity solution. For the low-performance market a single receiver can be used. For the high-performance market multiple receivers can be tied together to achieve the performance benefits associated with antenna diversity. When implementing a multi-chip diversity architecture, a synchronous transmission between chips is typically required, hence a clock signal generally must be transmitted along with the data.
FIG. 1 illustrates a block diagram of a traditional multi-chip diversity architecture 100 having a crystal oscillator connected to every receiver chip. A crystal oscillator uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is used to provide a stable clock signal and to stabilize frequencies for radio transmitters and receivers. In the multi-chip diversity architecture 100, multiple receiver chips 104A-N are connected to achieve the performance benefits associated with antenna diversity. The multi-chip diversity architecture 100 includes antennas 102A-N and receiver chips 104A-N. The receiver chips 104A-N include crystal oscillators 106A-N, tuners 108A-N, and demodulators 110A-N. The antennas 102A-N receive wireless signals. The crystal oscillators (XO) 106A-N generate signals at frequencies that ideally would be equivalent but in reality differ by tens or hundreds of parts-per-million (PPM). The tuners 108A-N receive and amplify the transmitted signal.
There are several disadvantages of the traditional multi-chip diversity architecture. In the traditional multi-chip diversity architecture 100, an independent crystal oscillator (XO) 106A-106N must be connected to each of the receiver chips 104A-N. Crystal oscillators are expensive components, and thus the bill of materials (BOM) cost is high for the multi-chip diversity architecture 100. Further, a reference clock is also required to be transmitted along with diversity data. The clock signal between chips 104A-104N is at least twice the data frequency. This high frequency signal can cause spurious emissions that can couple with the RF portion of the chip and reduce performance. Further, transmitting a clock signal between two chips increases chip overhead because this signal does not contain data. In addition, the multi-chip diversity architecture 100 is susceptible to frequency variations between a transmitter and a receiver that may lead to loss of synchronization.
Picture-in-Picture (PIP) is a feature of a television receiver in which one program is displayed on a full screen and one or more other programs are displayed in inset windows. In mobile television standards such as DVB-T and ISDB-T, the audio and video data are contained in a transport stream. The transport stream is composed of transport stream packets where each transport stream packet is labeled with a Program ID (PID). This PID indicates the contents of the transport stream packets. To implement PIP in a mobile television, a first receiver has to receive a first program composed of a first PID set and a second receiver has to receive a second program composed of a second PID set. A challenge to implementing PIP in mobile television is that when the first PID set and second PID set are merged and contain common PIDs, there is no way to distinguish whether the common PIDs belong to the first program or the second program.
Accordingly, there remains a need for an architecture that connects multiple chips using a single shared crystal oscillator thereby eliminating the frequency offset between receivers, reducing the bill of materials, and eliminating the need to transmit the reference clock between receivers. In addition, this architecture would also support PIP for mobile television by distinguishing the PIDs that are common between programs, thereby avoiding collisions between common PIDs.